The present invention relates to a method of controlling a laser power for writing data on an optical disk, e.g., CD-R (Compact Disk-Recordable), CD-RW (Compact Disk-ReWritable), and an optical disk player employing the method.
Many types of optical disk players, e.g., CD-R players, CD-RW players, have been used for writing data on optical disks.
In some optical disk players, linear velocity for writing data is maintained at a prescribed velocity so as to write data on an optical disk with fix pit density. This control manner is called CLV (Constant Linear Velocity). In the CLV manner, data are written in an inner part of the optical disk with a high rotational speed of the optical disk; and data are written in an outer part of the optical disk with a low rotational speed thereof.
These days, high speed writing is required. To accelerate the writing speed by the CLV manner, the rotational speed of the optical disk is merely accelerated, so that the rotational speed is too fast to write data in the inner part of the optical disk. Namely, data cannot be securely written in the inner part of the optical disk.
This problem of the CLV manner was solved by a zone CLV manner, in which data can be written in the inner part of the optical disk without over-accelerating the rotational speed of the optical disk and total writing time can be shortened.
In the zone CLV manner, data are written in the inner part of the optical disk with fixed low linear velocity, so the rotational speed for writing data in the inner part is equal to that of the CLV manner. The rotational speed of the optical disk is accelerated, by stages, with moving a data writing part toward an outer edge of the optical disk.
The zone CLV will be explained with reference to FIG. 10.
In the example shown in FIG. 10, data are written in an inner part of an optical disk 10 with 16× linear velocity; after the laps of prescribed time, data are written in an intermediate part thereof with 20× linear velocity; and after the laps of another prescribed time, data are written in an outer part thereof with 24× linear velocity.
As described above, the rotational speed for writing data in the inner part is equal to a proper speed of the CLV manner, so total writing time can be shortened without writing errors in the inner part.
In the conventional optical disk player, a data writing test or an optimum power control (OPC) test is executed in a power calibration area (PCA) 9 (see FIG. 10), which is located in an inner most part of a recording face of the optical disk, when data are written on the optical disk so as to adjust laser power for writing data to optimum power.
A method of setting the laser power of the optical disk will be explained.
Firstly, the optical disk player reads an absolute time in pregroove (ATIP) from the optical disk. A manufacturer of the optical disk has previously written data of the optical disk, e.g., a type of the disk, in the ATIP.
The optical disk player reads the data of the disk, e.g., the name of the manufacturer, a type of the optical disk, from the ATIP, then retrieves recommended laser power of the disk from a data table on the basis of the data. The data table has been previously stored in the optical disk player.
The optical disk player executes the OPC test with increasing and decreasing the laser power with respect to the recommended laser power. The written test data are read so as to check up-down symmetry of waveforms of light intensity of reflected laser beams. The laser power whose up-down symmetry is the best of all is selected and set as the optimum laser power of the disk.
The optical disk player writes data with the optimum laser power determined by the OPC test in the innermost PCA 9.
However, in the optical player employing the zone CLV manner, the linear velocity for writing data in the outer part is accelerated, so even if the laser power is determined by the OPC test in the PCA 9 located in the innermost part of the optical disk 10, the determined power is not optimum in the outer part thereof.
In the example shown in FIG. 10, the laser power is determined, by the OPC test, with 16× linear velocity. But data are written in the intermediate part with 20× linear velocity and written in the outer part with 24× linear velocity. Optimum laser power for 20× and 24× linear velocity are greater than that for 16× linear velocity.
Even if the laser power shifts from the optimum laser power, data can be written with the shifted power. However, the actual laser power is not optimum, so quality and reliability of written data must be low. In some cases, the written data cannot be read.